1. Field of the Invention
This invention relates generally to the treatment of diseased or traumatized intervertebral discs, and more particularly, to the use of engineered disc tissues in conjunction with such treatment.
2. Related Art
Intervertebral discs provide mobility and a cushion between the vertebrae. At the center of each disc is the nucleus pulposus, which in the adult human, is composed of cells and an insoluble extra-cellular matrix that is produced by the nucleus itself. The extracellular matrix is composed of collagen, proteoglycans, water, and noncollagenous proteins.
The cells of the nucleus pulposus have chondrocyte-like features. Blood vessels do not course into the nucleus pulposus. Rather, the cells of the nucleus pulposus of the adult human obtain nutrients and eliminate waste by diffusion through blood vessels in the endplates of the vertebrae adjacent to the disc.
The nucleus pulposus is surrounded by the annulus fibrosis, which is composed of cells (fibrocyte-like and chondrocyte-like), collagen fibers, and non-fibrillar extra-cellular matrix. The components of the annulus are arranged in 15-25 lamellae around the nucleus pulposus.
To date, the treatment of degenerative disc disease has relied for the most part on eliminating the defective disc or disc function. This may be accomplished by fusing the vertebra on either side of the disc. In terms of replacement, most prior-art techniques use synthetic materials to replace the entire disc or a portion thereof or harvested chondrocyte cells from a patient's own disk.
Unfortunately, disc replacement using synthetic materials does not restore normal disc shape, physiology, or mechanical properties. Synthetic disc replacements tend to wear out, resulting in premature failure. The problems associated with the wear of prosthetic hip and knees are well known to those skilled in orthopedic surgery. A more desirable approach for treating degenerative disc disease therefore lies in treatments that preserve disc function. If disc function could be restored with biologic replacement or augmentation, the risk of premature wear out would be minimized, if not eliminated.
A draw back with the known approach of harvesting chondrocyte cells from a disc for use in other disc is the additional risk inherent with medical procedures on a health disc. Even if cells are harvested from a diseased disc for later re-implantation in the same disc, this would necessitate multiple procedures on an already injured disc. Similarly, there are risks involved with rejection of cells that are harvested from cadavers or donors. Therefore, what is needed is a method and approach to heal an intervertebral disc with chondrocyte cells while reducing the medical risk associated with known approaches.